Characteristics of CuInSe2 Bridgman ingots grown with sodium

Crystals of CuInSe2 were grown by a horizontal Bridgman method for the first time with metallic sodium. The amount of sodium was varied with levels at 0.05, 0.25 and 2 at. % approximately. However, as the sodium content was increased, the crystalline quality decreased. Hot probe measurements showed that the ingots grown with higher sodium content (0.25 and 2 at. %) were n-type, while the ingot with about 0.05 at. % was p-type. Electron probe microanalysis and an Auger profile showed no detectable sodium (i.e. < 0.1 at. %) in the ingots, even up to 2 at. % added to the melt. X-ray Laue back reflection, performed on the as-grown surface of the p-type CuInSe2 ingot, confirmed the region to be single crystal. Powder X-ray diffraction patterns confirmed the chalcopyrite structure for all the ingots grown with sodium. Resistivity and carrier mobility in these ingots were obtained by Hall effect measurements. Metallic sodium was also introduced into already-grown CuInSe2 monocrystals within a sealed glass ampoule and the characteristics of these samples were also analyzed.